Recently there has been considerable interest within the detergents industry in the production of detergent powders by means of processes involving the neutralization of a liquid acid precursor of an anionic surfactant with a solid water-soluble alkaline inorganic material, for example sodium carbonate. Such processes are sometimes referred to as in-situ neutralization processes. They have the advantage that by means of such processes detergent powders may be prepared without the use of a spray-drying tower, whereby substantial savings on capital and energy costs can be achieved.
Various in-situ neutralization processes have been described in the art. For example, GB-A-2 166 452 (Kao) discloses a process whereby an alkyl sulphonic acid, sodium carbonate and water are mixed in a strongly shearing apparatus to form a solid mass which is subsequently cooled and pulverized. The obtained powder is then granulated in a separate processing step.
GB-A-2 221 695 (Unilever) discloses a batch process for preparing a high bulk density detergent powder whereby a detergent acid is gradually added over a period of several minutes to a solid water-soluble inorganic material in a Fukae-mixer. Subsequently, the product is granulated in the presence of a liquid binder.
EP-A-342 043 (Procter and Gamble) discloses a process for preparing a detergent component whereby zeolite, sodium carbonate and linear benzene sulphonic acid are fed continuously into a high intensity Lodige mixer. The contact time is said to be relatively short in comparison to the reaction time required for complete neutralization of the acid, and therefore the powder is placed subsequently in a batch mixer and provided with gentle agitation for 5 more minutes.
The above in-situ neutralization processes have the disadvantage that they involve several processing steps in order to arrive at a granular detergent compound, and that the time required to obtain neutralization of the acid anionic surfactant precursor is in the order of several minutes.
It is an object of the present invention to provide a simple and effective continuous in-situ neutralization process for preparing a granular detergent component or compound, in particular having a high level of anionic surfactant.
We have now surprisingly found that by means of the essentially single-step process of the invention a granular detergent compound or component may be prepared in continuous way whereby a degree of neutralization of at least 80% can be achieved, provided that the particle moisture content is maintained at values between 5 and 15%.